Method and device for producing a structured varnish surface

ABSTRACT

The invention relates to a method for producing a structured, at least partly optically transparent varnish surface on a surface of a substrate board, preferably of a wood material board, having a decoration. The steps of the method include applying a transparent or at least partly transparent varnish to an applicator roll thereby producing a structured varnish surface and transferring the structured varnish surface to a substrate board having a decoration. The varnish is applied to the applicator roll by a plurality of digitally controlled nozzles in a distribution defining a structure and/or is transformed on the applicator roll into a distribution defining a structure. Furthermore, a device for carrying out the method is described.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is the United States national phase of InternationalApplication No. PCT/EP2013/054510 filed Mar. 6, 2013, and claimspriority to German Patent Application No. 10 2012 103 491.5 filed Apr.20, 2012, the disclosures of which are hereby incorporated in theirentirety by reference.

BACKGROUND OF THE INVENTION

Field of the Invention

The invention relates to a method and to a device for producing astructured, at least partly optically transparent varnish surface on thesurface of a substrate board, preferably of a wood material board, whichhas a decoration.

Description of Related Art

There are various methods for producing floor, wall or ceiling panelsand furniture construction panels with decorative surfaces. In additionto methods in which decorative surfaces are produced on wood materialboards by coating said boards with printed, resin-impregnated paper(decor paper), methods are also known for printing a decoration, inparticular a wood decoration, directly onto wood material boards.

For example, WO 2006/002917 A2 by the Applicant describes a method forproducing a wood material board having a decorated surface. In thisknown method, a surface of the wood material board, which has alreadybeen ground and is to be provided with a decoration, in particular witha wood decoration, is primed, then smoothed and subsequently printeddirectly in the gravure printing method by means of printing rollers(printing cylinders), to produce the decoration.

To produce panels with decorative surfaces, digital printing methods arealso used in addition to roller printing methods. Thus for example, WO98/26936 A1 discloses a method for producing resin-impregnated decorpapers for coating substrate boards. In this method, a paper is printedby a digital printer, in particular by a laser printer. The decor paperis pressed onto the substrate board in a hot press, for example in ashort-cycle press, the resin which has impregnated the paper beingthereby cured. The substrate boards coated with the decor paper(laminates) are intended in particular for furniture construction.

To protect the decoration against abrasive wear, the decor paper or thedecoration printed directly onto the substrate board is provided with atransparent sealing layer.

The sealing layer of the decorative surfaces produced thus is usuallystructured such that it has a three-dimensional surface structure in theend. The three-dimensional structure improves the haptic effect of thedecorative surface. The haptic impression produced by the structureddecorative surface thereby corresponds to the surface character to beimitated, for example a porous wood surface.

To produce structured surfaces on wood material boards provided with adecoration, structured pressing plates, structured pressing belts orembossing rolls are used in the prior art. Furthermore, structuredvarnish applicator rolls are also used for this purpose. The productionof these plates, belts and rolls is associated with considerable costs.Furthermore, changing said plates, belts and rolls is verytime-consuming, which is a disadvantage in the case of a singleproduction plant in which wood material boards are to be produced withdifferent decorations and correspondingly different surface structures.

To solve this problem, it has been proposed to produce the surfacestructures by directly applying varnish to the board-shaped workpiecesby means of digital print heads. In this respect, the print headsoperate according to a jet printing method known from ink-jet printers.For this purpose, they are arranged in one or more rows transversely tothe feed direction of the workpiece and at a relatively short distanceabove said workpiece (cf. DE 10 2009 044 802 A1 and EP 2 218 520 A2).

However, a problem which arises during the operation of these knowndigital applicator devices is the risk of collisions which can occur atthe digital print heads when there are unevennesses in the board-shapedworkpieces, for example during cupping of the boards and/or if there areforeign bodies on the boards.

SUMMARY OF THE INVENTION

On this basis, the object of the present invention was to provide amethod and a device of the type mentioned at the outset, which avoid theabove-mentioned disadvantages.

The method according to the invention is characterised in thattransparent or at least partly transparent varnish is applied to anapplicator roll to produce the structured varnish surface and saidapplicator roll transfers the varnish to the surface of the substrateboard having a decoration, the varnish being applied to the applicatorroll in a distribution defining a structure by a plurality of digitallycontrolled nozzles and/or being transformed on the applicator roll intoa distribution defining a structure.

According thereto, the device according to the invention is fitted withan applicator roll for transferring a structured, preferably locallyvarying varnish surface to the surface of the substrate board having adecoration, the applicator roll being allocated a plurality of digitallycontrolled nozzles which are configured to apply transparent or at leastpartly transparent varnish to the applicator roll in a distributiondefining a structure and/or are configured to transform on theapplicator roll a transparent or at least partly transparent varnish,applied to the applicator roll as a varnish film, in a distributiondefining a structure.

Since according to the invention, the nozzles are not arranged at ashort distance above the board-shaped workpiece and the structuredvarnish surface is applied by the applicator roll, the nozzles areprotected from collisions which can happen if they are arranged at ashort distance above the board-shaped workpiece and the board-shapedworkpieces are uneven, for example cupped, or there are foreign bodieson the workpieces.

Whereas when structured embossing rolls in particular are used, thesurface structure producible thereby is typically repeated on theboard-shaped workpiece, the solution according to the inventionbasically makes it possible to produce a “continuous”, non-repetitivethree-dimensional surface structure. The length of a surface structurewhich does not have repetitions and can be produced by the methodaccording to the invention is restricted in practical terms only by themaximum length of the board-shaped workpiece.

Furthermore, the present invention allows the use of a smooth, standardapplicator roll, i.e. an applicator roll which has a smooth or slightlystructured lateral surface, typically a regularly structured lateralsurface. A smooth standard applicator roll of this type is considerablycheaper than a structured pressing plate or an engraved varnishapplicator roll.

A preferred configuration of the invention provides that the varnish isapplied to the applicator roll in such a distribution and/or istransformed on the applicator roll into such a distribution that thestructure, resulting from this distribution, of the structured varnishsurface produced on the surface of the substrate board defines poreswhich match the decor image of the decoration. In this manner, athree-dimensional surface structure which is adapted to the decoration,for example a wood, tile or natural stone decoration, is produced on theboard-shaped workpiece.

A further preferred configuration of the invention provides that beforethe varnish is transferred to the substrate board, the decor image ofthe decoration or a guide mark placed on the substrate board is detectedby an optical scanning device and measuring signals generated by thescanning device are used to control the digitally controlled nozzles. Inthis manner, the three-dimensional surface structure can beautomatically adapted to the decor image, particularly even when thedecor image itself changes according to a random principle. For example,the decoration, preferably a wood decoration, can be printed accordingto the invention by a printer device having digital print heads, inparticular ink-jet print heads, the print heads being controlled by acomputer or the like such that the decor image in its entirety or atleast a region of the decor image varies according to a randomprinciple.

A further advantageous configuration of the invention is characterisedin that the digitally controlled nozzles which are used are digitallycontrolled gas nozzles, preferably compressed air nozzles. By means ofsuch gas nozzles or compressed air nozzles a film of at least partlytransparent varnish, applied to the applicator roll, can be transformedinto a distribution defining a three-dimensional structure. In thisrespect, regions in the varnish film are displaced by jets of gas orcompressed air, thereby producing a three-dimensional structure. Forthis purpose, a plurality of gas or compressed air nozzles arepreferably arranged in a plurality of rows along the axis of theapplicator roll and are controllable independently of one another. Thenozzles of adjacent rows are preferably arranged axially offset to oneanother. In any case, the gas jets or air jets, generated by thenozzles, are thereby able to act on the applicator roll or on a film ofvarnish applied thereto in a switchable pattern.

The variant of the solution according to the invention, in which a filmof at least partly transparent varnish applied to the applicator roll istransformed into a distribution, defining a three-dimensional structure,by digitally controlled gas- or compressed air nozzles or jets of gas orcompressed air, has several advantages over digital print heads whichoperate according to the ink-jet printing method. A significantadvantage is in particular that gas or compressed air nozzles are notsusceptible to wear or are hardly subject to wear compared to varnishjet print heads and are thus very easy to maintain. In contrast, varnishjet print heads are at great risk of becoming blocked. Thesusceptibility to wear thereof is also relatively high. The specificlocal displacement of a film of varnish applied to the applicator rollby gas- or compressed air nozzles according to the solution variant ofthe invention allows the addition of particles which increase abrasionresistance in the varnish used to produce the three-dimensional surfacestructure. Accordingly, a preferred configuration of the inventionprovides that the varnish contains hard particles, preferably corundumparticles. However, in the case of varnish jet print heads, it isvirtually impossible to use a varnish containing hard particles due tothe print head wear and to the risk of blockage increased thereby.Furthermore, digital gas or compressed air nozzles suitable for thesolution variant according to the invention are much more cheaplyavailable than digital varnish jet print heads.

Furthermore, tests have shown that the solution variant according to theinvention and characterised by the use of digital gas or compressed airnozzles allows significantly higher print speeds than the variant usingonly conventional varnish jet print heads.

A further advantageous configuration of the invention is characterisedin that the varnish applied to the applicator roll is pre-dried orpre-cured thereon or in that associated with the applicator roll is aradiation source or a heating device, which is configured to pre-dry orpre-cure on the applicator roll the varnish which has been appliedthereto. This counteracts a run (flow) of the three-dimensional varnishstructure produced on the applicator roll, as a result of which theresolution (definition) of the structured varnish surface produced onthe board-shaped workpiece can be improved.

A further preferred configuration of the invention provides that theapplicator roll is rubberised and/or bowed. This configuration alsoplays a part in improving the resolution of the structured varnishsurface produced on the board-shaped workpieces. An applicator rollsleeve consisting of rubber or of a rubber-like material counteracts aflow of the varnish structure produced on the applicator roll and cancompensate for unevennesses in the board-shaped workpiece to be printed.A bowed configuration of the applicator roll furthers the achievement ofa uniform vertical distribution of the varnish structure over the widthof the applicator roll.

In the following, the invention will be described in more detail withreference to schematic drawings illustrating different embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side view of a device or installation having a plurality ofprint stations for producing board-shaped products having a decoratedsurface;

FIG. 2 shows a first embodiment of an applicator device according to theinvention; and

FIG. 3 shows a second embodiment of an applicator device according tothe invention.

DESCRIPTION OF THE INVENTION

FIG. 1 shows a device or installation for producing board-shapedproducts, for example furniture construction boards or floor, wall orceiling panels, having a decorated surface.

A plurality of board-shaped workpieces 1 are arranged on a conveyor belt2 and are individually fed successively to various processing stations3, 4, 5 and 6. The feed direction of the workpieces 2 is indicated by anarrow and runs from left to right. Instead of a plurality of singleworkpieces 1, one large-area workpiece or a continuously producedworkpiece can also be processed, which is divided into individual boards(blanks) after being processed as described in the following. Theconveyor belt speed or feed rate of the workpieces 1 is, for example,within a range of from 1 to 120 m/min.

The board-shaped workpiece 1 acts as a substrate and can therefore alsobe called a substrate board.

The workpiece or substrate board 1 is produced from wood material, fromlaminate and/or from at least one compact board. Compact boards areproduced from resin-impregnated cellulose webs which are pressed inlaminate presses under high pressure and at elevated temperatures.However, the substrate boards 1 are preferably ground wood materialboards, for example chipboard, medium-density fibreboard (MDF),high-density fibreboard (HDF) or hardboard.

After an optional brushing station (not shown) which removes impuritiesor grinding dust which may be present, fillers are applied in severalstages, preferably by applicator rolls (not shown), an intermediatedrying procedure being carried out after each stage. A primer coat keptin the basic colour of a subsequently printed-on decoration is thenapplied, again in several stages, to the thus present substrate board 1by rolls (not shown) and here again a partial drying is carried outafter each application.

The primed substrate board 1 is then preferably smoothed. This isperformed, for example, using heated polished steel rolls (not shown)which are operated over the width of the substrate board 1 and pressedagainst said substrate board 1 at a peripheral rotational speed greaterthan or less than the feed rate of the substrate boards 1. Thereafter,the substrate board 1 processed thus exhibits over its entire upper sidea surface which is even and uniform in colour, gloss level andstructure.

Directly following the optional smoothing device (not shown), adecoration (decor image), for example a wood, natural stone or tiledecoration, is printed onto the substrate board 1. The decor image ispreferably printed onto said board 1 by one or more print rollassemblies 3.1, 4.1. The respective print roll assembly 3.1, 4.1 istypically constructed from an engraved print roll (print cylinder) 3.11,4.11 with inking and dampening rolls and a blanket cylinder 3.12, 4.12with a counter-pressure cylinder. This printing method is also known asindirect gravure printing.

Instead of one or more print roll assemblies 3.1, 4.1, according to theinvention it is also possible to use a digital printer device (notshown), in particular an ink-jet printer device, to print a desireddecor image onto the substrate boards 1. The digital printer device ispreferably controlled such that the decor image is varied so that nosubstrate boards 1 or practically no substrate boards 1 are producedwith identical decor images. For this purpose, the digital printerdevice is connected, for example, to a computer which varies the size,shape and/or position of one or more decor image elements, for examplethe image of a wood grain, of heartwood and sapwood, of a knot (knotcross section), resin galls, burrs, age rings, burrows (for examplewoodworm holes/passages), nail heads, screw heads, etc, according to therandom principle and controls the digital print heads of the printerdevice accordingly.

Post-processing devices 3.2, 4.2 are arranged downstream of the digitalprinter device or print roll assemblies 3.1, 4.1. The respectivepost-processing device 3.2, 4.2 can carry out a drying or partial dryingof the printed decor image, for example by a stream of hot air or byhigh-energy and/or electromagnetic radiation, in particular UVradiation.

Following the digital printer device or print roll assembly 4.1 or thepost-processing device 4.2 is optionally at least one processing station5 which applies a sealing layer (wear-protection layer) to thedecoration.

A transparent UV-curable varnish coating is preferably applied in atleast two stages as the sealing of the decoration. The sealing varnishcan contain corundum particles and/or other particles which increase thewear resistance. If the decorative boards 1 to be produced are boardswhich are not exposed to a high abrasive stress, for example furnitureparts, particularly back walls of cupboards, then the sealing varnishcan also be free from corundum particles or other particles whichincrease wear resistance. Alternatively or in addition towear-resistance-increasing particles, the sealing varnish can containfurther additives, for example scratch-resistance-increasing additivesand/or antistatic agents.

In processing station 5, a substantially full-surface coating of aUV-curable, transparent sealing varnish is applied. For this purpose,processing station 5 has an applicator roll 5.1 which applies a uniformlayer of varnish to the upper side of the substrate board 1 printed withthe decoration. The applied coating is at least partly dried and curedin the post-processing device 5.2 connected downstream.

In a further processing station 6, an at least partly opticallytransparent, three-dimensionally structured layer of varnish 1.1 isapplied to the surface, having the decoration, of the substrate board 1,the decor image of which has preferably been coated with a transparentsealing layer. According to the invention, this is performed indirectlyby a plurality of digitally controlled nozzles 6.1 combined with anapplicator roll 6.2. The varnish used for this purpose is preferably aUV-curable varnish.

By means of a post-processing device 6.3, following applicator roll 6.2,then the last applied varnish layer 1.1 is at least partly cured, sothat the three-dimensional structure is fixed. Reference numeral 1′denotes the ready coated substrate board. Processing station 6 forproducing the structured, at least partly optically transparent varnishsurface 1.1 can be realised in different embodiments.

In the embodiment shown in FIG. 2, a plurality of digitally controllednozzles 6.1 as print heads (varnish jet nozzles) is associated withapplicator roll 6.2. The nozzles or print heads 6.1 are arranged in atleast one row and preferably cover the entire roll width (axial rolllength). Depending on the desired print speed, a plurality of rows ofprint heads can also be provided, which is indicated in FIGS. 1 and 2 bya dotted row of print heads. In this respect, the print heads 6.1 of onerow are preferably arranged offset to the print heads 6.1′ of the row ofprint heads running parallel thereto, i.e. they are arranged in the gapsbetween the print heads of the parallel row of print heads. The printheads 6.1, 6.1′ are positioned at a short distance above the applicatorroll 6.2, whereas the applicator roll 6.2 delivers the printed-onstructure varnish to the substrate board 1 by contact therewith. Thelateral surface of applicator roll 6.2 is substantially smooth orslightly structured. Furthermore, applicator roll 6.2 is preferablyrubberised and bowed. The bowing, i.e. the specifically barrel-shapedbulge of applicator roll 6.2 towards the centre thereof, compensates thedeflection of roll 6.2 which, in the case of a purely cylindricallyshaped roll, would result in an application thickness which would not beuniform over the width.

Analogously to the indirect gravure printing of the decor image, thethree-dimensional structure is thus not printed directly onto thesubstrate board 1, but is printed digitally onto applicator roll 6.2which then transfers the printed-on structure to substrate board 1.

The digital control commands for producing the structure and matchingthe decor image can be provided in a data record or are calculated orgenerated using the decor image read in by an optical scanning device(not shown). For this purpose, the decor image is localised on thesubstrate board 1, for example by a camera system (not shown), and thezero point is calculated or determined for printing the sleeve of theapplicator roll 6.2. In this way, it can be ensured that thethree-dimensional varnish surface 1.1 with its varnish pores presenttherein, which is produced, matches the decor image, for example a wooddecor image, on substrate board 1. Specialists also call this a“synchronous varnish pore” or a “synchronous surface structure”.

FIG. 3 is a sketch of a second embodiment of the device according to theinvention. In this embodiment, the varnish for producing the surfacestructure is not applied to applicator roll 6.2 by varnish jet printheads (varnish jet nozzles), but by a metering roll 6.4 and/or by adoctor (not shown). The metering roll 6.4 or doctor produces a film ofvarnish 6.5 of a defined layer thickness on applicator roll 6.2.

The varnish film 6.5 is then partly displaced on applicator roll 6.2 bystreams of gas, preferably by streams of compressed air, and is therebytransformed into a three-dimensional structure. For this purpose,digitally controlled gas nozzles or compressed air nozzles 6.1 arearranged above and/or at applicator roll 6.2. The nozzles 6.1 arearranged in at least one row which extends over the roll width, i.e.along the rotational axis of the applicator roll. A plurality of rows ofnozzles is preferably provided (cf. FIG. 1; 6.1, 6.1′), which define adigitally switchable nozzle pattern.

Here again, the lateral surface region of applicator roll 6.2 receivingthe varnish is substantially smooth or slightly structured. Theapplicator roll is also preferably rubberised and/or bowed.

Arranged upstream of applicator roll 6.2 in the feed direction of thesubstrate board 1 is an optical scanning device (not shown) whichdetects the decor image or a guide mark placed on the substrate board 1.The scanning device is connected to a control device (not shown) whichdigitally controls the nozzles 6.1, 6.1′, subject to the measuringsignals generated by the scanning device.

The applicator roll 6.2 can be allocated a radiation source or a heatingdevice 6.6, which is configured to pre-dry or pre-cure the varnish,applied and structured on the applicator roll 6.2, on said applicatorroll 6.2.

The realisation of the invention is not restricted to theabove-described embodiments. In fact, numerous variants are possible,which use the invention set out in the accompanying claims, even in afundamentally different form. Thus for example, it also lies within thescope of the invention to realise the application of the decoration(decor image) to the substrate board 1 by pressing on resin-impregnateddecor paper. In particular, it lies within the scope of the invention tocombine different features of the described embodiments with oneanother.

The invention claimed is:
 1. A method for producing a structured, atleast partly optically transparent varnish surface on a surface of asubstrate board comprising the steps of: applying a transparent or atleast partly transparent varnish as a film of varnish to an applicatorroll, transforming the film of varnish on the applicator roll, by aplurality of digitally controlled nozzles, into a distribution defininga three dimensional structure, and transferring the structured varnishedsurface by the applicator roll to the substrate board having adecoration.
 2. The method according to claim 1, wherein the varnish istransformed into such a distribution on the applicator roll that thestructure resulting from the distribution of the structured varnishsurface produced on the surface of the substrate board defines poreswhich match a decor image of the decoration.
 3. The method according toclaim 1, wherein before the varnish is transferred to the substrateboard a decor image of the decoration or a guide mark placed on thesubstrate board is detected by an optical scanner, and measuring signalsgenerated by the optical scanner are used to control the digitallycontrolled nozzles.
 4. The method according to claim 1, wherein thevarnish applied to the applicator roll is pre-dried or pre-cured on theapplicator roll.
 5. The method according to claim 1, wherein the varnishis applied as the film of varnish to the applicator roll by a meteringroll and/or by a doctor.
 6. The method according to claim 1, wherein theapplicator roll comprises a substantially smooth applicator rollvarnish-receiving lateral surface region.
 7. The method according toclaim 1, wherein the applicator roll is a rubberised and/or bowedapplicator roll.
 8. The method according to claim 1, wherein the varnishcontains hard particles.
 9. A device for producing a structured, atleast partly optically transparent varnish surface on a surface of asubstrate board, comprising: an applicator roll for transferring astructured varnish surface to a surface of a substrate board having adecoration; and a plurality of digitally controlled nozzles wherein thenozzles are configured to transform on the applicator roll a transparentor at least partly transparent varnish, which has been applied to theapplicator roll as a film of varnish, into a distribution defining athree-dimensional structure.
 10. The device according to claim 9,wherein the digitally controlled nozzles are arranged in at least onerow along the rotational axis of the applicator roll.
 11. The deviceaccording to claim 9 wherein the device further comprises an opticalscanner, wherein the optical scanner is arranged upstream of theapplicator roll in a feed direction of the substrate board to detect adecor image of the decoration or a guide mark placed on the substrateboard, wherein the optical scanner is connected to a controller, andwherein the controller digitally controls the nozzles, subject to themeasuring signals generated by the scanner.
 12. The device according toclaim 9, wherein the digitally controlled nozzles are formed as gasnozzles.
 13. The device according to claim 9, further comprising aradiation emitter or a heater, wherein the radiation emitter or theheater is associated with the applicator roll and configured to pre-dryor pre-cure the varnish applied and structured on the applicator roll.14. The device according to claim 9, wherein a metering roll and/or adoctor, are associated with the applicator roll to produce the film ofvarnish on the applicator roll.
 15. The device according to claim 9,wherein the applicator roll comprises a substantially smoothvarnish-receiving lateral surface region.
 16. The device according toclaim 9, wherein the applicator roll is rubberised and/or bowed.
 17. Themethod according to claim 1, wherein the digitally controlled nozzlesare formed as digitally controlled gas nozzles.
 18. A device forproducing a structured, at least partly optically transparent varnishsurface on a surface of a substrate board, comprising: an applicatorroll for transferring a structured varnish surface to a surface of asubstrate board having a decoration; and a plurality of digitallycontrolled nozzles wherein the nozzles are configured to transform onthe applicator roll a transparent or at least partly transparentvarnish, which has been applied to the applicator roll as a film ofvarnish, into a distribution defining a structure, wherein the devicefurther comprises an optical scanner, wherein the optical scanner isarranged upstream of the applicator roll in a feed direction of thesubstrate board to detect a decor image of the decoration or a guidemark placed on the substrate board, wherein the optical scanner isconnected to a controller, and wherein the controller digitally controlsthe nozzles, subject to the measuring signals generated by the scanner.